1. Technical Field
The present disclosure relates to a thin film transistor substrate and a liquid crystal display having the same.
2. Description of the Related Art
Liquid crystal displays (“LCD”s) typically include lower and upper substrates having field-generating electrodes, e.g., a pixel electrode and a common electrode, respectively, and a liquid crystal layer interposed between the lower and upper substrates. LCDs display an image in such a way that orientations of liquid crystal molecules in the liquid crystal layer are determined by applying a voltage to the field generating electrodes to generate an electric field across the liquid crystal layer and polarization of incident light is controlled.
Among the various kinds of LCDs, a vertical alignment (“VA”) mode LCD, in which major axes of liquid crystal molecules are aligned vertically to the upper and lower substrates while an electric field is not applied, is currently the focus of much attention due to the high contrast ratio and easy implementation of a wide viewing angle. To ensure the wide viewing angle in the VA mode LCD, a method of forming a cutout or a protrusion in/on a field-generating electrode is used. The cutout and the protrusion can control the orientation direction of the liquid crystal molecules. Accordingly, the tilting angles of the liquid crystal molecules can be distributed in various directions using the cutout and the protrusion to ensure a wide viewing angle
To more improve a wide viewing angle of the VA mode LCD, a patterned vertical alignment (“PVA”) mode LCD and a multi-domain vertical alignment (“MVA”) mode LCD have been proposed. In the PVA mode LCD, a common electrode is patterned to align liquid crystal molecules in different directions due to the patterned common electrode, thereby noticeably improving the viewing angle. In the MVA mode LCD, a protrusion formed on an orientation film distorts the direction of magnetic field to align liquid crystal molecules in different directions, thereby improving the viewing angle significantly.
In addition, another LCD has recently been introduced, in which microslits are formed in a pixel electrode to divide a liquid crystal layer into four domains. Specifically, in this LCD, a storage electrode line is formed to cross the center of a pixel region defined by a gate line and a data line, and a plurality of microslits are formed in the pixel electrode from horizontal and vertical parts. The horizontal and vertical parts respectively divide the pixel region into halves vertically and horizontally, resulting in four sub pixel regions. Herein, the storage electrode line and the horizontal part overlap each other, and a thin film transistor (“TFT”) is formed to be closer to one side of the pixel region. The data line and the pixel electrode are insulated from each other by a thin inorganic insulation layer.
The above-described LCD has a low aperture ratio because the pixel electrode does not overlap the data line. Thus, to obtain a high aperture ratio, the pixel electrode should overlap the data line. To this end, a thick low-dielectric-constant insulation layer such as an organic layer should be formed on the data line. However, this may lead to a decrease in storage capacitance due to the thick low-dielectric-constant insulation layer provided between the storage electrode line and the pixel electrode even though the storage electrode line and the vertical part overlap each other.
Further, it may be difficult to drive the above-described LCD at a frame refresh rate of 120 Hz using a dot inversion driving method. The driving method of the LCD at a frame refresh rate of 120 Hz is a very effective method of minimizing LCD motion blur, and thus it is being rapidly standardized. However, if the frame refresh rate increases from 60 Hz to 120 Hz, a turn-on time of each gate line may decrease to half or less compared to 60 Hz. Therefore, the dot inversion driving method may not be available for high-resolution LCDs such as Full-HD (high definition) LCDs. Moreover, it may also be necessary to form a low-resistance interconnection, for example, a copper interconnection having the specific resistance of 2.5 μΩcm or smaller. However, it may be very difficult to form a low-resistance interconnection, as the LCD becomes greater and requires higher resolution than ever before.
Moreover, when the LCD is driven in dot inversion driving manner, a data line voltage may swing to a maximum of 15 V or higher at every one horizontal time, thereby possibly increasing the temperature of a source driver IC. A vertical inversion driving method is a possible way to avoid a high resistance and the increase in the temperature of the source driver IC. In the vertical inversion driving method, a capacitance variation between the data line and the pixel electrode may become very sensitive depending on an overlay offset between the data line and the pixel electrode in comparison with the dot inversion driving method. Consequently, as a result, this may produce vertical crosstalk, which in turn may lead to display defects.
Moreover, as the TFT is disposed closer to one side of the pixel region in the LCD, the aperture ratio of a pixel in an odd-numbered row may be different from that of a pixel in an even-numbered row. Therefore, two horizontal lines are displayed due to the difference in aperture ratio.